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<p>Ferromagnetic superconductors are exceptionally rare because the strong ferromagnetic exchange field usually destroys singlet superconductivity. EuFe<sub>2</sub>(As<sub>1−<i>x</i></sub>P<sub><i>x</i></sub>)<sub>2</sub>, an iron-based superconductor with a maximum critical temperature of 25 K, uniquely exhibits full coexistence with ferromagnetic order below <i>T</i><sub>FM</sub>&#xa0;≃ 19 K. The interplay leads to narrowing of ferromagnetic domains at higher temperatures and spontaneous nucleation of vortices/antivortices at lower temperatures. Here we demonstrate how the underlying magnetic structure controls the superconducting vortex dynamics in applied magnetic fields. Just below <i>T</i><sub>FM</sub> we observe a pronounced peak in the creep activation energy, and magnetic force microscopy measurements reveal the presence of very closely spaced (<i>w</i>&#xa0;≪&#xa0;<i>λ</i>) vortex clusters. We attribute these observations to the formation of vortex polarons, for which we present a theoretical description. In contrast, we link strong magnetic irreversibility at low temperatures to a critical current governed by giant flux creep over an activation barrier for vortex-antivortex annihilation near domain walls. Our work suggests new routes for the magnetic enhancement of vortex pinning with important applications in high-current conductors.</p><p></p>

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Magnetically controlled vortex dynamics in a ferromagnetic superconductor

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年5月31日

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  • Joseph Alec Wilcox,
  • Lukas Schneider,
  • Estefani Marchiori,
  • Vadim Plastovets,
  • Alexandre Buzdin,
  • Pardis Sahafi,
  • Andrew Jordan,
  • Raffi Budakian,
  • Tong Ren,
  • Ivan Veshchunov,
  • Tsuyoshi Tamegai,
  • Sven Friedemann,
  • Martino Poggio,
  • Simon John Bending

摘要

Ferromagnetic superconductors are exceptionally rare because the strong ferromagnetic exchange field usually destroys singlet superconductivity. EuFe2(As1−xPx)2, an iron-based superconductor with a maximum critical temperature of 25 K, uniquely exhibits full coexistence with ferromagnetic order below TFM ≃ 19 K. The interplay leads to narrowing of ferromagnetic domains at higher temperatures and spontaneous nucleation of vortices/antivortices at lower temperatures. Here we demonstrate how the underlying magnetic structure controls the superconducting vortex dynamics in applied magnetic fields. Just below TFM we observe a pronounced peak in the creep activation energy, and magnetic force microscopy measurements reveal the presence of very closely spaced (w ≪ λ) vortex clusters. We attribute these observations to the formation of vortex polarons, for which we present a theoretical description. In contrast, we link strong magnetic irreversibility at low temperatures to a critical current governed by giant flux creep over an activation barrier for vortex-antivortex annihilation near domain walls. Our work suggests new routes for the magnetic enhancement of vortex pinning with important applications in high-current conductors.